Integrated micro electro-mechanical system and manufacturing method thereof

ABSTRACT

In the manufacturing technology of an integrated MEMS in which a semiconductor integrated circuit (CMOS or the like) and a micro machine are monolithically integrated on a semiconductor substrate, a technology capable of manufacturing the integrated MEMS without using a special process different from the normal manufacturing technology of a semiconductor integrated circuit is provided. A MEMS structure is formed together with an integrated circuit by using the CMOS integrated circuit process. For example, when forming an acceleration sensor, a structure composed of a movable mass, an elastic beam and a fixed beam is formed by using the CMOS interconnect technology. Thereafter, an interlayer dielectric and the like are etched by using the CMOS process to form a cavity. Then, fine holes used in the etching are sealed with a dielectric.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of nonprovisional U.S. applicationSer. No. 12/216,359 filed Jul. 2, 2008, which is a Continuation ofnonprovisional U.S. application Ser. No. 11/208,740 filed Aug. 23, 2005.Priority is claimed based on U.S. application Ser. No. 12/216,359 filedJul. 2, 2008, which claims the priority of U.S. application Ser. No.11/208,740 filed Aug. 23, 2005, which claims the priority of JapanesePatent Application JP 2005-050541 filed on Feb. 25, 2005 and JapanesePatent Application JP 2005-226233 filed on Aug. 4, 2005, the contents ofwhich are hereby incorporated by reference into this application.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to micro electro-mechanical systems (MEMS)and a manufacturing method thereof. More particularly, the presentinvention relates to a technology effectively applied to an integratedmicro electro-mechanical system in which a semiconductor integratedcircuit and the MEMS are integrated.

BACKGROUND OF THE INVENTION

By using the micro-fabrication technology which has realized theimprovement in performance and increase in integration density of thesemiconductor integrated circuit, the micro electro-mechanical system(hereinafter, referred to as MEMS) technology for forming a mechanicalsensor such as a pressure sensor and a acceleration sensor, a miniaturedswitch, miniature mechanical parts such as a resonator or an oscillator,and a mechanical system has been developed. The MEMS is broadlyclassified into a bulk MEMS which is formed by processing a siliconsubstrate itself and a surface MEMS which is formed by repeatedlydepositing and patterning thin films on a surface of a siliconsubstrate. The manufacturing process of the surface MEMS is close to themanufacturing process of semiconductor integrated circuits. The MEMStechnologies described above are discussed in pp. 1158 to 1165 of volume73 (issue 9) of “Applied Physics” (Japan Society of Applied Physics(JSAP), September, 2004).

The U.S. Pat. No. 6,635,506 discloses the technology for preciselyforming a shape of a cavity by using a sacrificial layer when formingthe cavity used for the MEMS.

The U.S. Pat. No. 6,667,245 discloses an example in which a switch isformed as the MEMS. Also, it mentions that it is possible to form theswitch at low cost by using the standard technology for forming amultilayer interconnect of an integrated circuit to form the switch.

The US Patent Application Publication No. 2004/0145056 describes thatthe MEMS is formed by using a metal layer and a sacrificial layer formedby the standard manufacturing technology of CMOSFET (Complementary MetalOxide Semiconductor Field Effect Transistor, referred to as CMOS,hereinafter).

The U.S. Pat. No. 5,596,219 discloses the technology for monolithicallyforming an integrated circuit and a sensor (actuator). This sensor isformed on a sensor layer made of polysilicon by using the surfacemicro-machine technology.

SUMMARY OF THE INVENTION

For example, in the application of MEMS to a sensor, the mechanicaldeformation of a structure due to the external force or the like isconverted into the electrical signal as the piezoresistance change andthe capacitance change and then outputted. Further, in general, theabove-mentioned output is signal-processed by a semiconductor integratedcircuit (LSI: Large Scale Integration, LSI includes CMOS.). Also, in theapplication of MEMS to an oscillator, the input and output of theoscillators are connected to the RF-IC (Radio-Frequency integratedcircuits). As described above, the MEMS is used in combination with theLSI in many cases. In addition, since the operation of the MEMS is notlimited to the mechanical operation, the conversion of the differentphysical values (electrical signal and mechanical deformation in manycases) is required in most of the applications thereof. This conversionmechanism is called a transducer.

As described above, when the MEMS is used in combination with the signalprocessing LSI, since each of them is formed on the separate chips, theminiaturization of the entire system is difficult. Since both the MEMSand the LSI are usually formed on a silicon substrate, the directiontoward the monolithic integration of them on the same substrate isnatural, and it has already been applied in some products.

For example, an acceleration sensor or a vibration gyroscope using amass composed of a poly-crystalline silicon film with a thickness ofabout 2 to 4 μm is integrated with an analog circuit such as acapacitance-voltage converter or an operation amplifier circuit. Asensor mechanical part (arranged on a silicon substrate with a gap) andan analog circuit part are arranged in the different (adjacent) regionson the substrate plane. The sensor mechanical part is entirely coveredand sealed with a cover.

Also, a digital mirror device, in which movable metal films each havinga reflection surface are arranged in a matrix form, and the directionsof each film are electrostatically controlled to turn on/off the light,thereby realizing a display device, has been produced. The upper part ofthe device is sealed with a transparent plate which transmits light.

Furthermore, a technology for forming a RF-MEMS (switch, filter) on aLSI by the so-called copper-damascene interconnect process has beenreported. In this technology, both the movable part and the cavity partare formed by the damascene process. In addition, the sealing methodafter forming the movable part is also described. Further, the method offorming a ME mechanical part and a transducer (signal unit) by using themultilayer interconnect of a LSI has been reported.

All of the cases described above belong to the category of the surfaceMEMS. However, the technology for integrating the bulk MEMS with a LSIhas been also reported. In the bulk MEMS, since the silicon wafer itselfbecomes a movable part, the bonding with other wafer (substrate) isrequired for the sealing and the packaging.

The first problem to be solved is that the special cavity formationprocess and the special sealing process are necessary in theconventional MEMS. More specifically, in the manufacture of the MEMS, aspecial technology is required in addition to the normal manufacturingtechnology of CMOS. In particular, in the case of an oscillator, thevacuum sealing is necessary to obtain the large vibration value Q, andthe air tightness is important for maintaining the properties for a longtime. This is true of the case of the integrated MEMS in which the LSIis mounted together with a MEMS. Also in the example in which themultilayer interconnect is used to form the mechanical part, except forthe cases of special application, it is preferable to seal the entirethereof. In this case, it is necessary to bond the substrate on whichthe MEMS is formed and another substrate to be a lid. Also, in theexample in which the cavity is fabricated through the damascene process,a special process such as the process of embedding a sacrificial layerinto an interlayer dielectric is required. As described above, thespecial technology in addition to the normal CMOS manufacturingtechnology is required in the conventional MEMS manufacturing process.

The second problem is that a film much thicker than a film used in thestandard LSI is necessary in order to form a mass with a sufficient massrequired in an acceleration sensor and a gyroscope. This is particularlydifficult in the case of the integrated MEMS in which a LSI is mountedtogether with a MEMS for the following reasons. First, it is difficultto form a thick film with a controlled mechanical stress in the standardLSI process. Even if possible, it is difficult to combine it with thefine CMOS process from the viewpoint of the temperature condition of thethermal treatment. Also, in the case where the SOI (Silicon onInsulator) is used, a special process such as the deep trench etching isnecessary, and thus, the process is complicated and the cost isincreased.

The third problem is that the manufacturing process of the integratedMEMS in which a LSI is mounted together with a MEMS is complicated, andthe chip area is increased.

An object of the present invention is to provide a technology capable ofmanufacturing an integrated MEMS without using a special processdifferent from the normal manufacturing technology of a semiconductorintegrated circuit, in the manufacturing technology of an integratedMEMS in which a semiconductor integrated circuit (CMOS and others) and amicro machine are monolithically integrated on a semiconductorsubstrate.

Also, another object of the present invention is to provide a technologycapable of easily manufacturing a mass with a sufficient mass requiredin an acceleration sensor and a gyroscope at low cost, in themanufacturing technology of an integrated MEMS including an accelerationsensor or a gyroscope.

Also, still another object of the present invention is to provide atechnology capable of simplifying a manufacturing process of anintegrated MEMS to reduce the manufacturing cost of a product.

Further, still another object of the present invention is to provide atechnology capable of miniaturizing an integrated MEMS.

The above and other objects and novel characteristics of the presentinvention will be apparent from the description of this specificationand the accompanying drawings.

The typical ones of the inventions disclosed in this application will bebriefly described as follows.

An integrated micro electro-mechanical system according to the presentinvention is the integrated micro electro-mechanical system, in which amicro machine formed by using a manufacturing technology of asemiconductor integrated circuit and a semiconductor integrated circuitare formed on a semiconductor substrate, and the micro machinecomprises: (a) a sealed cavity formed by removing a part of aninterlayer dielectric formed between the interconnects; and (b) amechanical structure formed in the cavity, wherein the cavity is formedby using a technology for forming an interconnect of a MOSFET and issealed by using the technology for forming an interconnect of a MOSFET.

Also, a manufacturing method of an integrated micro electro-mechanicalsystem according to the present invention is the manufacturing method ofan integrated micro electro-mechanical system, in which a micro machineformed by using a manufacturing technology of a semiconductor integratedcircuit and a semiconductor integrated circuit are formed on asemiconductor substrate, and the method comprises the steps of: (a)forming a mechanical structure which is a part of the micro machine; (b)forming a layer covering the mechanical structure; (c) forming a cavityin which the mechanical structure is placed; and (d) sealing the cavity,wherein the step (a), the step (b), the step (c) and the step (d) areperformed by using a technology for forming an interconnect of a MOSFET.

The first primary characteristic of the present invention is that acavity for placing a mechanical structure of a MEMS (micro machine) isformed by using a standard CMOS manufacturing process or a standardinterconnect process which is a part of the CMOS manufacturing process(without using a special sealing process). More specifically, first, amovable part also functioning as an electrode which is a part of themechanical structure of a MEMS is formed in an interlayer dielectric byusing the CMOS process (multilayer interconnect process). Then, afterforming a (metal) thin film layer with micro holes therein, theinterlayer dielectric around the movable part also functioning as anelectrode is etched and removed through the micro holes, and then, themicro holes are finally sealed.

At this time, the structure of the micro machine is placed in the cavityformed by removing a part of the interlayer dielectric formed in themultilayer interconnects below the thin film layer. As the thin filmlayer, a material with the sufficiently low etching rate to the etchingof the interlayer dielectric (for example, upper interconnect layer) isused.

After the finish of the etching of the interlayer dielectric, the microholes for etching formed in the thin film layer are sealed by depositinga thin film (CVD dielectric or the like) having relatively isotropicdeposition characteristics on the thin film layer. The thin filmformation and the etching to remove the interlayer dielectric areperformed within the range of the normal CMOS process. The movable partalso functioning as an electrode formed in the cavity is formed so as tocontain any one of a metal film, a silicon-germanium film, a siliconnitride film, a silicon oxide film, a single crystal silicon film, apolysilicon film, an amorphous silicon film and a polyimide film.

In addition, the second primary characteristic of the present inventionis that, by forming one integral mechanical structure (including a massand a movable part considered as a mechanically integral structure)using a plurality of LSI layers or interconnect layers, a movable masswith a sufficient mass required in an acceleration sensor and agyroscope can be formed through the standard interconnect process of theCMOS process. The movable part of the mechanical structure is preferablyformed in a cavity and is fixed to an interlayer dielectric surroundingthe cavity by a (elastically) deformable LSI material or metalinterconnects. The mechanical structure is designed so that themechanical characteristics thereof are determined based on thedimensions of the structure itself and do not depend on the shape of thecavity. More specifically, the mechanical structure is provided with (1)a fixed part which is fixed to an interlayer dielectric surrounding acavity and has an enough size substantially considered to be elasticallyundeformed, (2) a movable part and (3) an elastically deformable partwhich connects the fixed part and the movable part. By doing so, thedimensional accuracy of the cavity does not influence the mechanicalcharacteristics of the MEMS. Therefore, the high dimensional accuracy ofthe cavity is not required in comparison to the case where themechanical characteristics of the structure depend on the shape of thecavity. Usually, the dimensional accuracy of the structure is definedwith the accuracy of the interconnect pattern of a LSI. Since thisdimensional accuracy is generally much higher than the process accuracyof the bulk MEMS in the conventional technology, the highly accuratemechanical characteristics can be assured.

Since the structure is formed by using the interconnect layers, thestructure itself has not only the mechanical function as a mass but alsothe electrical function as an electrode and an interconnect. Theactuation and the sensing are performed by the electrostatic force andcapacitance between the electrically independent electrode fixed to aninterlayer dielectric and a movable part also functioning as anelectrode. By using the movable part of the integral structure as amass, for example, an acceleration sensor and a vibration gyroscope(angle rate sensor) are realized. The mechanical connection between themovable part and the surrounding interlayer dielectric (fixed part andelastically deformable part, for example, beam) and the electricalconnection (interconnect, actuator capacitor and detecting capacitor)can be made through separate layers constituting the LSI. By sandwichingthe movable part between the multilayer interconnects to restrict themovable range of the movable part, it becomes possible to improve thereliability.

Also, the present invention is characterized in that a MEMS such as avibration sensor, an acceleration sensor, a gyroscope, a switch and anoscillator is integrated with a LSI, and the mechanical structure of theMEMS is formed from the same layer as the interconnect layer of a LSI(including pad). Alternatively, it is characterized in that a MEMS isstacked and formed on (an area overlapping with) the interconnect of aLSI.

The effect obtained by the representative one of the inventionsdisclosed in this application will be briefly described as follows.

Since a LSI (including CMOS) and a MEMS can be monolithically integratedthrough the standard CMOS process (LSI process), it is possible toachieve the miniaturization and the cost reduction of the integratedMEMS.

BRIEF DESCRIPTIONS OF THE DRAWINGS

FIG. 1 is a schematic diagram showing the manufacturing process of anacceleration sensor according to the first embodiment of the presentinvention;

FIG. 2 is a schematic diagram showing the manufacturing process of theacceleration sensor subsequent to FIG. 1;

FIG. 3 is a schematic diagram showing the manufacturing process of theacceleration sensor subsequent to FIG. 2;

FIG. 4 is a schematic diagram showing the manufacturing process of theacceleration sensor subsequent to FIG. 3;

FIG. 5 is a schematic diagram showing the manufacturing process of theacceleration sensor subsequent to FIG. 4;

FIG. 6 is a schematic diagram showing the manufacturing process of theacceleration sensor subsequent to FIG. 5;

FIG. 7 is a schematic diagram showing the manufacturing process of theacceleration sensor subsequent to FIG. 6;

FIG. 8 is a schematic diagram showing the manufacturing process of theacceleration sensor subsequent to FIG. 7;

FIG. 9A to FIG. 9C are plan views showing the major layers constitutingthe acceleration sensor, respectively;

FIG. 10 is a block diagram showing the circuit configuration of thecapacitance detecting circuit;

FIG. 11 is a schematic diagram showing the cross-sectional structurewhen the acceleration sensor and the pressure sensor are simultaneouslyformed;

FIG. 12 is a schematic diagram showing the cross-sectional structure ofthe acceleration sensor according to the second embodiment;

FIG. 13A and FIG. 13B are plan views showing the major layersconstituting the acceleration sensor, respectively;

FIG. 14 is a schematic diagram showing the cross-sectional structurewhen the acceleration sensor and the pressure sensor are simultaneouslyformed;

FIG. 15A to FIG. 15C are plan views schematically showing theconfiguration and the basic operation of the MEMS switch according tothe third embodiment;

FIG. 16A to FIG. 16D are schematic diagrams showing a part of themanufacturing process of the MEMS switch, respectively;

FIG. 17A and FIG. 17B are plan views showing the major layers of theMEMS switch, respectively;

FIG. 18 is a schematic diagram showing the manufacturing process of anacceleration sensor according to the fourth embodiment;

FIG. 19 is a schematic diagram showing the manufacturing process of theacceleration sensor subsequent to FIG. 18;

FIG. 20 is a schematic diagram showing the manufacturing process of theacceleration sensor subsequent to FIG. 19;

FIG. 21 is a schematic diagram showing the manufacturing process of theacceleration sensor subsequent to FIG. 20;

FIG. 22 is a schematic diagram showing the manufacturing process of theacceleration sensor subsequent to FIG. 21;

FIG. 23 is a schematic diagram showing the manufacturing process of theacceleration sensor subsequent to FIG. 22;

FIG. 24 is a schematic diagram showing the manufacturing process of theacceleration sensor subsequent to FIG. 23;

FIG. 25 is a schematic diagram showing the manufacturing process of theacceleration sensor subsequent to FIG. 24;

FIG. 26A to FIG. 26C are plan views showing the major layersconstituting the acceleration sensor, respectively;

FIG. 27A and FIG. 27B are cross-sectional views showing the accelerationsensor according to the modification examples of the fourth embodiment,respectively;

FIG. 28 is a schematic diagram showing the manufacturing process of anacceleration sensor according to the modification example of the fourthembodiment;

FIG. 29 is a schematic diagram showing the manufacturing process of theacceleration sensor subsequent to FIG. 28;

FIG. 30 is a schematic diagram showing the manufacturing process of theacceleration sensor subsequent to FIG. 29;

FIG. 31 is a schematic diagram showing the manufacturing process of theacceleration sensor subsequent to FIG. 30;

FIG. 32 is a schematic diagram showing the manufacturing process of theacceleration sensor subsequent to FIG. 31;

FIG. 33 is a schematic diagram showing the manufacturing process of theacceleration sensor subsequent to FIG. 32;

FIG. 34 is a schematic diagram showing the manufacturing process of anangle rate sensor (vibration gyroscope) according to the fifthembodiment;

FIG. 35 is a schematic diagram showing the manufacturing process of theangle rate sensor subsequent to FIG. 34;

FIG. 36 is a schematic diagram showing the manufacturing process of theangle rate sensor subsequent to FIG. 35;

FIG. 37 is a schematic diagram showing the manufacturing process of theangle rate sensor subsequent to FIG. 36;

FIG. 38 is a schematic diagram showing the manufacturing process of theangle rate sensor subsequent to FIG. 37;

FIG. 39 is a schematic diagram showing the manufacturing process of theangle rate sensor subsequent to FIG. 38;

FIG. 40 is a schematic diagram showing the configuration of the anglerate sensor according to the fifth embodiment;

FIG. 41A and FIG. 41B are plan views showing the operation of the anglerate sensor according to the fifth embodiment, respectively;

FIG. 42 is a schematic diagram showing the manufacturing process of anangle rate sensor according to the sixth embodiment;

FIG. 43 is a schematic diagram showing the manufacturing process of theangle rate sensor subsequent to FIG. 42;

FIG. 44 is a schematic diagram showing the manufacturing process of theangle rate sensor subsequent to FIG. 43;

FIG. 45 is a schematic diagram showing the manufacturing process of theangle rate sensor subsequent to FIG. 44;

FIG. 46 is a schematic diagram showing the manufacturing process of theangle rate sensor subsequent to FIG. 45;

FIG. 47 is a schematic diagram showing the manufacturing process of theangle rate sensor subsequent to FIG. 46;

FIG. 48A and FIG. 48B are plan views showing the major layersconstituting the angle rate sensor, respectively;

FIG. 49A and FIG. 49B are plan views showing the operation of the anglerate sensor according to the sixth embodiment, respectively;

FIG. 50 is a schematic diagram showing the manufacturing process of anangle rate sensor according to the modification example of the sixthembodiment;

FIG. 51 is a schematic diagram showing the manufacturing process of theangle rate sensor subsequent to FIG. 50;

FIG. 52 is a schematic diagram showing the manufacturing process of theangle rate sensor subsequent to FIG. 51;

FIG. 53 is a schematic diagram showing the manufacturing process of theangle rate sensor subsequent to FIG. 52;

FIG. 54 is a schematic diagram showing the manufacturing process of theangle rate sensor subsequent to FIG. 53;

FIG. 55 is a diagram showing the configuration of the gas pressuremonitoring system for tire seen from the bottom surface of anautomobile;

FIG. 56 is a block diagram of a tire pressure measurement module;

FIG. 57 is a block diagram of a in-vehicle unit;

FIG. 58 is a diagram showing the configuration of an anti-skid devicefor a vehicle seen from the bottom surface of an automobile;

FIG. 59 is a block diagram of an anti-skid control circuit;

FIG. 60 is a block diagram showing an air suspension control unit; and

FIG. 61 is a side view of the vehicle showing the configuration of anair suspension control unit seen from the side of an automobile.

DESCRIPTIONS OF THE PREFERRED EMBODIMENTS

In the embodiments described below, the invention will be described in aplurality of sections or embodiments when required as a matter ofconvenience. However, these sections or embodiments are not irrelevantto each other unless otherwise stated, and the one relates to the entireor a part of the other as a modification example, details, or asupplementary explanation thereof.

Also, in the embodiments described below, when referring to the numberof elements (including number of pieces, values, amount, range, and thelike), the number of the elements is not limited to a specific numberunless otherwise stated or except the case where the number isapparently limited to a specific number in principle. The number largeror smaller than the specified number is also applicable.

Further, in the embodiments described below, it goes without saying thatthe components (including element steps) are not always indispensableunless otherwise stated or except the case where the components areapparently indispensable in principle.

Similarly, in the embodiments described below, when the shape of thecomponents, positional relation thereof and the like are to bementioned, the substantially approximate and similar shapes and the likeare included therein unless otherwise stated or except the case where itcan be conceived that they are apparently excluded in principle. Thiscondition is also applicable to the numerical value and the rangedescribed above.

In addition, components having the same function are denoted by the samereference symbols throughout the drawings for describing theembodiments, and the repetitive description thereof is omitted. Notethat hatching is used in some cases even in a plan view so as to makethe drawings easy to see.

Hereinafter, embodiments of the present invention will be described indetail with reference to the accompanying drawings.

In the embodiments described below, after fabricating transistors of aLSI on a silicon (Si) substrate, simultaneously with forming amultilayer interconnect on the transistors, a MEMS is formed in theinterlayer dielectric formed between the multilayer interconnect on thesame silicon substrate, and then, a cavity is formed and sealed.Alternatively, after forming a MEMS on a silicon substrate, a LSI isfabricated on the same silicon substrate, and then, a cavity is formedand sealed.

First Embodiment

In the first embodiment, the case where a single axis acceleration (orvibration) sensor is formed as the MEMS will be described.

FIG. 1 to FIG. 8 are schematic diagrams (cross-sectional views) showingthe manufacturing process of the integrated MEMS according to the firstembodiment. First, in accordance with the normal manufacturing processof a CMOS integrated circuit, transistors 102 for signal processing ofthe single axis acceleration sensor and contact holes 103 are formed ona silicon substrate (semiconductor substrate) 101 (FIG. 1). Next, byusing the manufacturing process of the CMOS integrated circuit, a firstlayer interconnect (M1 layer) 104 of the signal processing transistors102 and an etching stopper film 105 used in the etching for forming acavity (process described later) are formed (FIG. 2).

Next, through the normal process for manufacturing a CMOS integratedcircuit, a multilayer interconnect comprised of a second layerinterconnect (M2 layer) and a third layer interconnect (M3 layer)(second layer interconnect and third layer interconnect are not shown.)is formed, and the surface thereof is planarized by the normal chemicalmechanical polishing (CMP). Next, after forming an interlayer dielectric106, via holes 107 are formed in the interlayer dielectric 106 (FIG. 3).Then, according to need, a fourth layer interconnect (M4 layer) 108 isformed on the interlayer dielectric 106, and a movable mass (movablepart) 109 of the single axis acceleration sensor, an elastic beam alsofunctioning as interconnect (elastically deformable part) 110 and afixed beam (fixed part) 111 are formed on the interlayer dielectric 106(FIG. 4). More specifically, the mechanical structure constituting apart of the single axis acceleration sensor (movable mass, elastic beam,fixed beam) is formed. As described above, this structure is formed fromthe same layer as the interconnect (for example, fourth layerinterconnect 108) constituting the semiconductor integrated circuit.

Further, an interlayer dielectric 112 is formed so as to cover thestructure and the interlayer dielectric 112 is planarized according toneed by the CMP or the like (FIG. 5). Thereafter, a cavity cover film114 having fine (tiny) holes 113 for forming a cavity is formed from afifth layer interconnect (M5 layer) (FIG. 6). Then, the interlayerdielectric 112 and the interlayer dielectric 106 around the movable mass109 are etched and removed through the fine holes 113 to form a cavity115 (FIG. 7). At this time, since the etching stopper film 105 isformed, the etching does not reach below the etching stopper 105. Then,the fine holes 113 for forming a cavity are filled up with a dielectric116 to seal the cavity 115 (FIG. 8).

Note that tungsten (W) is used as a material of the first layerinterconnect 104 and the fourth layer interconnect 108, aluminum (Al) isused as a material of the second layer interconnect and the third layerinterconnect, and tungsten silicide (WSi) is used as a material of thefifth layer interconnect. The materials are not limited to them, but astacked film of an aluminum film and a titanium nitride (TiN) film canbe used as the first layer interconnect 104 and tungsten can be used asa material of the fifth layer interconnect. The advantage of using theabove-described materials for the first layer interconnect 104 and thefifth layer interconnect is that the etching selectivity (in etchingrates) between the interlayer dielectric 106 and the interlayerdielectric 112 can be sufficiently ensured in the etching for formingthe cavity 115.

Next, the configuration and operation of the single axis accelerationsensor according to the first embodiment will be described. FIG. 9A toFIG. 9C are schematic diagrams showing the structure pattern in each ofthe layers constituting the completed single axis acceleration sensor.The plan views of the M1 layer, the M4 layer and the M5 layer are shownin FIGS. 9A, 9B and 9C, respectively. In FIG. 9A, the etching stopperfilm 105 of the M1 layer functions as a capacitor lower electrode and isconnected by the first layer interconnect 104 to an integrated circuitincluding the signal processing transistors 102 integrated on the samesubstrate. In FIG. 9B, the movable mass 109 formed in the M4 layer isconnected to the fixed beam 111 via the elastic beam 110 formed in aspiral shape. The movable mass 109 functions as a capacitor upperelectrode and is electrically connected to the integrated circuitincluding the signal processing transistors 102 by the elastic beam 110,the fixed beam 111 and the fourth layer interconnect 108. The movablemass 109 formed in the cavity 115 is mechanically fixed to theinterlayer dielectric 112 via the elastic beam 110 and the fixed beam111. In this configuration, the movable mass 109 is moved in thedirection vertical to the paper of the drawing by the acceleration inthe direction vertical to the paper of the drawing. Therefore, thedistance between the capacitor upper electrode composed of the movablemass 109 and the capacitor lower electrode composed of the etchingstopper film 105 is changed and the interelectrode capacitance ischanged. By detecting this change in capacitance by the integratedcircuit including the signal processing transistors 102 (capacitancedetecting circuit), the acceleration can be detected as the change incapacitance. More specifically, the single axis acceleration sensoraccording to the first embodiment can detect the acceleration acting inthe direction vertical to the silicon substrate 101 (chip).

As shown in FIG. 9C, the cavity cover film 114 is formed in the M5layer, and the cavity cover layer 114 has the fine holes 113 used toform the cavity 115. The cavity 115 is formed by the etching through thefine holes 113. After forming the cavity 115, the fine holes 113 arefilled up.

As shown in FIG. 9B, the shape of the fixed beam 111 is designed so thata base part thereof is sufficiently thick to prevent the elasticdeformation even when the acceleration is applied to the movable mass109. On the other hand, the elastic beam 110 positioned at the center ofthe beam is designed so as to have the smaller width in comparison tothat of the fixed beam 111 and a sufficient length because of its spiralshape, and the desired elastic deformation occurs when a predeterminedacceleration is applied. Therefore, the mechanical characteristics ofthe single axis acceleration sensor are determined only by the patternshape and the thickness of the fixed beam 111, the elastic beam 110 andthe movable mass 109 in the M4 layer, and do not depend on thedimensions and the shape of the cavity 115. Since the dimensionalaccuracy of the fixed beam 111, the elastic beam 110 and the movablemass 109 is determined by the dimensional accuracy of the M4 layer(dimensional accuracy for forming the interconnect), it is veryaccurate. Meanwhile, since the dimensions and the shape of the cavity115 are determined by the etching of the interlayer dielectrics 106 and112, the accuracy thereof is not so high. However, it does not influencethe mechanical characteristics of the single axis acceleration sensoraccording to the first embodiment.

More specifically, the single axis acceleration sensor according to thefirst embodiment is designed so that the mechanical characteristics aredetermined by the movable mass 109, the elastic beam 110 and the fixedbeam 111. Therefore, the cavity 115 can be formed by the etchingtechnology (etching of interlayer dielectric itself) with lower accuracythan that of the normal manufacturing technology of a CMOS integratedcircuit, that is, the case where the mechanical characteristics of theMEMS are determined by the shape of the cavity 115.

On the contrary, in the technology of the U.S. Pat. No. 6,635,506, themechanical characteristics are influenced by the cavity. Therefore, itis necessary to form the cavity with high accuracy. For its achievement,a sacrificial layer made of a material different from that of theinterlayer dielectric is formed in the region of an interlayerdielectric for forming a cavity. As a result, the process for formingthe cavity is complicated.

Meanwhile, in the first embodiment, it is not necessary to form thecavity 115 with high accuracy. Therefore, the cavity 115 is formed bythe etching of the interlayer dielectrics 106 and 112 themselves throughthe fine holes 113 without using a sacrificial layer. Also, afterforming the cavity 115, the fine holes 113 are filled up by thedielectric 116 to seal the cavity 115. The deposition of the dielectric116 which is included in the normal manufacturing technology of a CMOSintegrated circuit is used also in this sealing process. Morespecifically, the process for forming and sealing the cavity 115 can besimplified in the first embodiment.

As described above, in the first embodiment, since the cavity 115 can beformed and sealed through the standard CMOS process, the special processfor forming and sealing the cavity (packaging process particular toMEMS) which is the major cause of the yield decrease and themanufacturing cost increase in the conventional MEMS manufacturingprocess becomes unnecessary. Therefore, according to the firstembodiment, it is possible to improve the yield, reduce themanufacturing (packaging) cost and improve the reliability. In addition,since the structure of the MEMS (single axis acceleration sensor) can beformed simultaneously with the formation of the interconnect of the LSI,the integration with the LSI can be facilitated.

Note that the planar shapes of the movable mass 109, the elastic beam110 and the fixed beam 111 are not limited to those shown in FIG. 9B.For example, the configuration in which a movable mass located at thecenter is supported by elastic beams provided at the four corners.

Next, the capacitance detecting circuit will be described. FIG. 10 is ablock diagram showing the circuit configuration of an integrated circuit(capacitance detecting circuit) including the signal processingtransistors 102.

In FIG. 10, the capacitance detected by an acceleration sensor 117 isconverted into voltage by a C-V (capacitance-voltage) conversion circuit118. Thereafter, the voltage converted by the C-V conversion circuit 118is amplified by an operation amplifier 119 and then digitized by an A-Dconversion circuit 120. Then, various types of correction such astemperature and amplifier characteristics are performed by a microprocessor 121 based on the data stored in a non-volatile memory 122, andit is outputted as the acceleration from an output interface circuit123. Note that the acceleration detecting accuracy can be furtherimproved by simultaneously detecting a suitable fixed referencecapacitance or capacitance change between the M5 layer and the movablemass 109 to use it as the difference input of the capacitance detectingcircuit.

Next, an application of the single axis acceleration sensor according tothe first embodiment will be described. The single axis accelerationsensor according to the first embodiment is mounted together with apressure sensor for a TPMS (tire pressure monitoring system). The singleaxis acceleration sensor detects the acceleration based on thedisplacement of a movable mass due to the centrifugal force from therotation of the tires and the vibration from the road surface, anddetermine the operational state of an automobile, that is, whether ornot the automobile is running or not. Then, based on the detectionresult of the single axis acceleration sensor, the frequency of datatransmission using RF such as the tire pressure information outputtedfrom the pressure sensor is determined. That is, by providing the singleaxis acceleration sensor, the frequency of RF transmission of tirepressure information detected by the pressure sensor can be increasedwhen the automobile is running, and the frequency of RF transmission oftire pressure information detected by the pressure sensor can be reducedwhen the automobile is not running. Consequently, the needless RFtransmission can be reduced and the lifetime of battery can be extended.

The pressure sensor can be formed through the interconnect processsimilar to the single axis acceleration sensor. FIG. 11 is across-sectional view showing the device in which the single axisacceleration sensor 130 according to the first embodiment and thepressure sensor 130 are formed at the same time.

A lower electrode 132 of the pressure sensor 131 is formed from the samelayer as the movable mass 109 of the single axis acceleration sensor130. An upper electrode 133 (also functioning as diaphragm film) of thepressure sensor 131 is formed from the same layer as the cavity coverfilm 114 (sealing film) of the single axis acceleration sensor 130. Theformation of the cavity 134 of the pressure sensor 131 and the formationof the cavity 115 of the single axis acceleration sensor 130 areperformed at the same time through fine holes 135 provided in the upperelectrode 133 of the pressure sensor 131 and the fine holes 113 providedin the cavity cover film 114 of the single axis acceleration sensor 130.Similarly, the sealing of the upper electrode 133 of the pressure sensor131 and the sealing of the cavity cover film 114 of the single axisacceleration sensor 130 are also performed at the same time. In thismanner, the pressure sensor 131 can be manufactured in parallel throughapproximately the same process as that of the single axis accelerationsensor 130 according to the first embodiment.

In the pressure sensor 131, the pressing force to the upper electrode133 shown in FIG. 11 is changed (position of the upper electrode 133 ischanged) along with the change in gas pressure around the pressuresensor 131. Therefore, the distance between the upper electrode 133 andthe lower electrode 132 is changed and the interelectrode capacitance ischanged. Consequently, in the pressure sensor 131, the gas pressure canbe detected by detecting this interelectrode capacitance.

Second Embodiment

In this second embodiment, a modification example of the above-describedfirst embodiment will be described. First, in the second embodiment, a2-axis acceleration sensor which detects the acceleration in twodirections within chip (directions orthogonal to each other) will bedescribed. In the acceleration sensor, it is necessary to ensure apredetermined amount of mass of the movable mass. Therefore, themechanical structure is formed from a pad layer with a relatively largethickness in the interconnect layers.

FIG. 12 is a schematic diagram showing the cross-sectional structure ofthe 2-axis acceleration sensor, and FIG. 13A and FIG. 13B are schematicdiagrams showing the configuration of the major layers. In FIG. 12, amovable mass 202, an elastic beam 203 (not shown in FIG. 12) and a fixedcapacitor plate (capacitance detecting electrode) 204 of the 2-axisacceleration sensor 201 are formed from the same metal layer as the padlayer 205 of the LSI in which they are monolithically integrated. The2-axis acceleration sensor 201 is formed on the normal LSI 206 and acavity 207 thereof is formed around the movable mass 202 and sealed inthe same manner as that of the first embodiment. However, when formingthe cavity 207, an etching stopper film 208 is formed by using anappropriate interconnect layer just below the cavity forming region.This etching stopper film 208 also functions as an electric shieldbetween the underlying LSI 206 (integrated circuit and multilayerinterconnect) and the 2-axis acceleration sensor 201. As describedabove, since the mechanical structure of the MEMS (2-axis accelerationsensor) can be formed and stacked on the LSI (interconnect part anddevice region), the miniaturization of a chip can be realized.

In the etching for forming the cavity 207, it is necessary to ensure thesufficient etching selectivity between the interlayer dielectric 210 tobe etched and the movable mass 202, the etching stopper film 208 and thecavity cover film 209 for sealing made of a pad layer material. In thiscase, the pad layer 205 is a stacked film formed by sandwiching analuminum (Al) film with a thickness of 1500 nm between titanium nitride(TiN) films each having a thickness of 100 nm. By doing so, in theetching for forming the cavity 207, the etching selectivity to theinterlayer dielectric 210 can be sufficiently ensured. If necessary, itis also possible to form sidewalls made of a titanium nitride film or asilicon nitride (SiN) film in order to prevent the side etching from theside of the aluminum film.

In order to seal the cavity 207 having an area large enough to includethe relatively large movable mass 202, it is necessary to ensure thesufficient strength of the cavity cover film 209. In this case, atungsten silicide (WSi) film with a thickness of 1 μm is used. In orderto prevent the adhesion and destruction of the cavity cover film 209 dueto the capillary force of the residual liquid in the cavity 207 in thedry process after the etching, the vapor-phase etching using vaporizedHF is used to form the cavity 207.

Next, the operation of the 2-axis acceleration sensor according to thesecond embodiment will be described. As shown in FIG. 13A, the movablemass 202 in the cavity 207 is fixed to the interlayer dielectric 210 viathe elastic beam 203 formed from the same layer. The interlayerdielectric 210 also functions as a fixed beam considered to beelastically undeformed. By forming the elastic beam 203 in a foldedshape as shown in FIG. 13A, the elastic beam 203 is elastically deformedby the force applied to the movable mass 202 and the two dimensionalposition of the movable mass 202 is changed in the cavity 207. Theamount of change is detected as the change in capacitance between amovable capacitor plate 211 formed at a part of the movable mass and afixed capacitor plate 204 fixed to the interlayer dielectric 210 andprotruding in the cavity 207. The movable capacitor plate 211 and thefixed capacitor plate 204 for detecting the displacement in the twodirections (x and y directions) within a chip are arranged in a combshape in which they are alternately formed in a lateral direction. Apair of fixed capacitor plates 204 sandwiching the one movable capacitorplate 211 are electrically independent from each other, and thecapacitance between the fixed capacitor plate 204 and the movable mass202 is detected separately. For example, when the movable mass 202 movesin the x direction, the distance between the movable capacitor plate 211and the fixed capacitor plate 204 arranged above and below is changed.More specifically, in the movable capacitor plate 211 and one pair offixed capacitor plates 204 arranged above and below, the distancebetween the movable capacitor plate 211 and one fixed capacitor plate204 is increased and the distance between the movable capacitor plate211 and the other fixed capacitor plate 204 is decreased. When thedistance is changed, the capacitance is also changed. Therefore, bydetecting the change in capacitance, the acceleration in the x directioncan be detected. Also, when the movable mass 202 moves in the ydirection, the distance between the movable capacitor plate 211 and thefixed capacitor plate 204 arranged side by side is changed. Morespecifically, in the movable capacitor plate 211 and one pair of fixedcapacitor plates 204 arranged side by side, the distance between themovable capacitor plate 211 and one fixed capacitor plate 204 isincreased and the distance between the movable capacitor plate 211 andthe other fixed capacitor plate 204 is decreased. Therefore, theacceleration in the y direction can be detected.

These fixed capacitor plates 204 and the movable mass 202 (including themovable capacitor plates 211) in the x and y directions are electricallyconnected independently to the signal processing integrated circuit(LSI) integrated on the same semiconductor substrate. When the movablemass 202 moves by the acceleration in an arbitrary direction of the twoaxes, the distance between the fixed capacitor plate 204 and the movablecapacitor plate 211 is changed and the interelectrode capacitance ischanged. By detecting the change in capacitance by the signal processingintegrated circuit (capacitance detecting circuit), the acceleration isdetected.

The shape of the beam is designed so that the base part thereof issufficiently thick in the cavity 207 to prevent the elastic deformationeven when the acceleration is applied to the mass (fixed part, fixedbeam). On the other hand, the center part of the beam is designed so asto have the smaller width in comparison to that of base part and asufficient length because of its folded shape, and the desired elasticdeformation occurs when a predetermined acceleration is applied(elastically deformable part, elastic beam 203). Therefore, themechanical characteristics are determined only by the planar patternshape and the thickness of the part of the beam and the movable mass 202exposed in the cavity 207, and do not depend on the dimensions and theshape of the cavity 207. Since the dimensional accuracy of the fixedbeam, the elastic beam 203 and the movable mass 202 is determined by thedimensional accuracy of the patterns of the interconnect layer and thevia layer, it is very accurate. Meanwhile, since the dimensions and theshape of the cavity 207 are determined by the etching of the interlayerdielectric 210, the accuracy thereof is not so high. However, it doesnot influence the mechanical characteristics of the 2-axis accelerationsensor according to the second embodiment.

FIG. 13B shows the cavity cover film 209 formed on the cavity 207, andfine holes 212 used to form the cavity 207 are formed in the cavitycover film 209. The fine holes 212 are sealed with a dielectric when theformation of the cavity 207 is finished.

Next, an example in which the 2-axis acceleration sensor according tothe second embodiment is formed simultaneously with the pressure sensoris shown in FIG. 14. FIG. 14 is a cross-sectional view of a compoundsensor in which the 2-axis acceleration sensor 201 according to thesecond embodiment is formed simultaneously with a pressure sensor 220similar to that in the first embodiment.

As shown in FIG. 14, the mechanical structure (movable mass 202, fixedcapacitor plate 204 and the like) of the 2-axis acceleration sensor 201is formed from the same layer as that of the pad layer 205, and aninterconnect 221 for connecting an upper electrode and an interconnect222 for connecting a lower electrode of the pressure sensor 220 areformed thereon. Subsequently, after forming an interlayer dielectric223, an opening for connecting upper electrode and an opening forconnecting lower electrode are provided on the pad layer 205.

Next, a lower electrode 224 of the pressure sensor 220 is formed and thelower electrode 224 is connected to the interconnect 222 for connectinga lower electrode. Subsequently, a dielectric (oxide film) pattern 225for forming a cavity of the pressure sensor 220 is formed. Then, a metalfilm (for example, tungsten film) to be the upper electrode (diaphragmfilm) 226 of the pressure sensor 220 and the cavity cover film 209 ofthe 2-axis acceleration sensor 201 is formed on the entire surface ofthe semiconductor substrate. Thereafter, after forming fine holes in themetal thin film on the cavity forming region of the pressure sensor 220and on the cavity forming region of the 2-axis acceleration sensor 201,the interlayer dielectric 223 and the dielectric pattern 225 are etchedthrough the fine holes. By doing so, the cavity 227 of the pressuresensor 220 and the cavity 207 of the 2-axis acceleration sensor 201 areformed. Subsequently, the fine holes formed in the metal thin film aresealed.

Thereafter, the metal thin film is patterned to form the upper electrode226 of the pressure sensor 220 and the cavity cover film 209 of the2-axis acceleration sensor 201. Then, a passivation film made of asilicon nitride film is deposited and an opening is formed on thepressure sensor 220 and the predetermined pad (not shown).

As described above, also in this second embodiment, the pressure sensor220 and the 2-axis acceleration sensor 201 can be formed almost at thesame time.

According to the second embodiment, since the movable mass 202 of the2-axis acceleration sensor 201 can be formed from the interconnect inthe same layer as the pad layer (relatively thick layer) 205, the massof the movable mass 202 can be greatly increased in comparison to thefirst embodiment. Therefore, it is possible to improve the sensitivityof the 2-axis acceleration sensor 201. Note that, also in the secondembodiment, the formation of the mechanical structure and the formationand sealing of the cavity of the 2-axis acceleration sensor can beperformed through the normal CMOS process. Therefore, the advantagessimilar to those of the first embodiment can be realized.

Third Embodiment

In this third embodiment, the MEMS switch mounted together with the LSIwill be described. In the third embodiment, the MEMS switch and theintegrated circuit are monolithically mounted by using the normalmanufacturing technology of a CMOS integrated circuit (interconnectprocess). Since the MEMS switch is formed on the multilayer interconnectof the integrated circuit, the increase of the chip area can beprevented. The MEMS switches are used to switch the circuit blocks andto switch the input/output RF devices and the antennas in accordancewith the RF (Radio Frequency) wireless communication system. By doingso, the connection to low-power-consumption wireless devices andantennas with small loss can be realized.

First, the function and basic operation of a MEMS switch 300 accordingto the third embodiment will be described. FIG. 15A to FIG. 15C are planviews schematically showing the configuration and the basic operation ofthe MEMS switch 300 according to the third embodiment.

The function of the MEMS switch 300 according to the third embodiment isto connect or disconnect the input to or from the output in response tothe control signal. The MEMS switch 300 has three states, that is, aconnection state, a disconnection state and a transition state. In theconnection state, as shown in FIG. 15C, two contacts 301 a and 301 b ofa central movable part 301 are in contact with a contact 302 a of aninput line 302 and a contact 303 a of an output line 303. Meanwhile, inthe disconnection state, as shown in FIG. 15A, the two contacts 301 aand 301 b of the central movable part 301 are not in contact with thecontact 302 a of the input line 302 and the contact 303 a of the outputline 303. In these connection state and disconnection state, the inputline 302 and the output line 303 of the MEMS switch 300 are electricallyconnected to the signal lines of each integrated circuit. Also, thetransition state shown in FIG. 15B is the state corresponding to thetransition from the connection state to the disconnection state or fromthe disconnection state to the connection state, in which the input line302 and the output line 303 of the MEMS switch 300 are electricallydisconnected from the signal lines of each integrated circuit and areconnected to the signal line from a switch control unit.

Next, the function of each component will be described. The input line302 is comprised of a fixed part (fixed beam) 306 fixed to an interlayerdielectric 305 formed so as to surround a cavity 304 and a movable part308 including an elastically deformable spring part 307 and the contact302 a. A part of the movable part 308 constitutes one electrode 309 a ofa comb-shaped displacement actuator 309. On the other hand, the otherelectrode 309 b of the comb-shaped displacement actuator 309 is fixed tothe interlayer dielectric 305.

The configuration of the output line 303 is almost symmetrical to thatof the input line 302. More specifically, the output line 303 iscomprised of a fixed part (fixed beam) 310 fixed to the interlayerdielectric 305 formed so as to surround the cavity 304 and a movablepart 312 including an elastically deformable spring part 311 and thecontact 303 a. A part of the movable part 312 constitutes one electrode313 a of a comb-shaped displacement actuator 313. On the other hand, theother electrode 313 b of the comb-shaped displacement actuator 313 isfixed to the interlayer dielectric 305.

In addition, the central movable part 301 is also comprised of almostthe same components, that is, it is comprised of a fixed part (fixedbeam) 314 fixed to the interlayer dielectric 305 formed so as tosurround the cavity 304 and a movable part 316 including an elasticallydeformable spring part 315 and the contacts 301 a and 301 b. Morespecifically, an interconnect having one end fixed to the interlayerdielectric 305 is electrically and mechanically connected to the movablepart 316 including the contacts 301 a and 301 b via the elasticallydeformable spring part 315. A part of the movable part 316 constitutesone electrode 317 a of a comb-shaped displacement actuator 317.Meanwhile, the other electrode 317 b of the comb-shaped displacementactuator 317 is fixed to the interlayer dielectric 305. Note that FIG.15A to FIG. 15C are schematic diagrams, and the planar configuration ofthe spring part and the actuator is simplified.

Next, the actual operation of the MEMS switch will be briefly describedwith using the transition from the disconnection state to the connectionstate as an example. In the disconnection state shown in FIG. 15A, thethree comb-shaped displacement actuators 309, 313 and 317 are notactuated, and no force is applied to any of the three spring parts 307,311 and 315. Therefore, the input line 302 and the output line 303 areswitched from the integrated circuit signal line to the actuator controlsignal line. Then, the voltage is applied between a pair of electrodes309 a and 309 b of the comb-shaped displacement actuator 309 provided inthe input line 302. By doing so, the movable part 308 iselectrostatically actuated and the contact 302 a of the input line 302is displaced to outside. Similarly, the voltage is applied between apair of electrodes 313 a and 313 b of the comb-shaped displacementactuator 313 provided in the output line 303. By doing so, the movablepart 312 is electrostatically actuated and the contact 303 a of theoutput line 303 is displaced to outside.

In this state, the central movable part 301 can move in a longitudinaldirection with no interference. Further, by applying the voltage betweena pair of electrodes 317 a and 317 b of the comb-shaped displacementactuator 317 provided in the central movable part 301, the centralmovable part 301 is electrostatically actuated and is displaced upward(FIG. 15B).

Subsequently, the movable part 308 of the input line 302 and the movablepart 312 of the output line 303 are returned to the initial positions.Thereafter, when the actuation of the comb-shaped displacement actuator317 of the central movable part 301 is stopped, the central movable part301 is fixed to the input line 302 and the output line 303 by the forceof the spring part 315. More specifically, the contacts 301 a and 301 bof the central movable part 301 are connected to the contact 302 a ofthe input line 302 and the contact 303 a of the output line 303,respectively (FIG. 15C). Thereafter, by switching the input line 302 andthe output line 303 to the integrated circuit signal line, it comes tothe connection state.

Next, the manufacturing process of the MEMS switch 300 according to thethird embodiment will be briefly described. Similar to the secondembodiment, the components of the MEMS switch 300 are formed from onlyone interconnect layer, and the manufacturing process thereof is almostidentical to that of the first and second embodiments. Morespecifically, the transistors and the multilayer interconnect are formedthrough the normal CMOS integrated circuit process, and the mechanicalstructure of the MEMS switch 300 is formed thereon by using the almostidentical method shown in the above-described second embodiment. Thatis, in the third embodiment, instead of forming the structure of theacceleration sensor, the structure of the MEMS switch 300 is formed.Similar to the second embodiment, this structure is formed with using apart of the uppermost layer of the multilayer interconnect. However, itis also possible to form the structure with using an intermediateinterconnect layer on the memory region in which the number ofinterconnects is small.

Also, when forming a cavity around the mechanical structure, a thin filmusing an interconnect layer is formed as an etching stopper film justbelow the structure in the cavity forming region. This thin filmfunctions as an electric shield for the transistors and the multilayerinterconnects formed below.

In the third embodiment, the electrical conduction must be obtained whenthe structures formed of the interconnects are connected. Therefore, itis necessary to prevent the adhesion of dielectrics on the surface ofthe structure. Also, it is also necessary to prevent the so-calledsticking in which the metal bodies are not separated after beingconnected to each other. For its achievement, in addition to the sealingprocess described in the first embodiment (refer to FIG. 8), thefollowing process shown in FIG. 16A to FIG. 16D must be performed.

FIG. 16A to FIG. 16D are schematic diagrams showing a part of themanufacturing process of the MEMS switch 300 according to the thirdembodiment, and FIG. 17A and FIG. 17B are schematic diagrams showing theconfiguration of the major layers constituting the MEMS switch 300. Asshown in FIG. 16A, an interconnect (not shown) and a structure 320 ofthe MEMS switch are formed by using the predetermined interconnectlayer. Then, an interlayer dielectric 321 is deposited on the structure320, and a thin film made of a similar interconnect material is formedon the interlayer dielectric 321. Thereafter, holes are formed in thisthin film to form a cavity cover film 322. The holes include at leasttwo types of holes, that is, fine holes 323 having a relatively smalldiameter (about 0.2 to 0.3 μm) and a larger hole 324 having a diameterlarger than that of the fine hole 323. The plan view of the cavity coverfilm 322 in which the fine holes 323 and the larger hole 324 are formedis shown in FIG. 17A. As shown in FIG. 17A, the fine holes 323 arearranged on the predetermined cavity forming region and the larger hole324 is provided at the position below which the structure is notpresent. Note that the dotted line represents the structure 320 formedbelow the cavity cover film 322 via the interlayer dielectric 321.

Next, the interlayer dielectric 321 around the structure 320 is etchedand removed through the fine holes 323 and the larger hole 324 to formthe cavity 325. The plan view showing the layer in which the structure320 is formed is shown in FIG. 17B. As shown in FIG. 17B, the cavity 325is formed in the interlayer dielectric 321, and the structure 320 isformed in the cavity 325.

Subsequently, the fine holes 323 are filled up with a dielectric 326having isotropic deposition characteristics (FIG. 16B). At this time,the dielectric 326 is also adhered to the surface of the structure 320made of, for example, metal due to the deposition gas getting in thecavity 325 through the fine holes 323. Therefore, when only the fineholes 323 are formed in the cavity cover film 322, the cavity 325 issealed while the dielectric 326 is adhered to the surface of thestructure 320. As a result, the electrical conduction cannot be obtainedwhen connecting the MEMS switch. However, the larger hole 324 is formedin addition to the fine holes 323 in the third embodiment. Since thislarger hole 324 is not filled up, the cavity 325 is not sealed yet.

Next, the dielectric 326 adhered to the surface of the structure 320 inthe cavity 325 is etched through the larger hole 324, and then, themetal surface after the etching is hydrophobically treated so as toprevent the sticking (FIG. 16C). Thereafter, a dielectric 327 isdeposited by the anisotropic CVD under the reduced pressure to close thelarger hole 324. In this manner, the cavity 325 is completely sealed(FIG. 16D).

As described above, according to the third embodiment, since it ispossible to remove the dielectric 326 formed on the surface of thestructure 320 in the sealing process of the cavity 325, the improvementof the reliability of the MEMS switch can be achieved. Note that, alsoin the third embodiment, the structure of the MEMS switch can be formedand the cavity can be formed and sealed through the CMOS process.Therefore, the advantages similar to those of the first embodiment canbe realized.

Fourth Embodiment

In this fourth embodiment, an example in which an integral movable partcomposed of a plurality of multilayer interconnects is used will bedescribed. As a problem of the acceleration sensor using the surfaceMEMS, the increase of the mass of the movable mass is relativelydifficult. This is because the thickness of the movable mass isdetermined by the thickness of the interconnect layer. In the fourthembodiment, the method and the structure capable of increasing the massof the movable mass will be described. In order to increase the mass ofthe movable mass, an integral structure composed of a plurality ofmultilayer interconnects is used as a movable part. It is possible tosimultaneously form the movable mass and the multilayer interconnects ofa LSI.

FIG. 18 to FIG. 25 are schematic diagrams for describing themanufacturing process of a 3-axis acceleration sensor according to thefourth embodiment, and FIG. 26A to FIG. 26C are schematic plan viewsshowing the configuration of each layer of the structure constitutingthe 3-axis acceleration sensor.

First, through the normal CMOS integrated circuit process, signalprocessing transistors 402 and contact holes 403 of the 3-axisacceleration sensor are formed on a silicon substrate 401 (FIG. 18).Next, through the similar CMOS integrated circuit process, a first layerinterconnect (M1 layer) 404 of the integrated circuit, a movable mass405 of the 3-axis acceleration sensor, an elastic beam 406 (not shown)also functioning as an interconnect electrically and mechanicallyconnected to the movable mass 405 and a lower electrode 407 describedlater are formed from the metal patterns (FIG. 19). A schematic diagramof the M1 layer pattern of the 3-axis acceleration sensor is shown inFIG. 26. In FIG. 26, the movable mass 405 is fixed to a fixed beam(interlayer dielectric) via the elastic beam 406.

Each of the elastic beam 406 and the lower electrode 407 is connected tothe predetermined interconnects of the signal processing transistors 402via the first layer interconnect 404 and the contact holes. Fine holes408 for removing the interlayer dielectric just below the movable mass405 in the latter process are formed in the movable mass 405.

Thereafter, after an interlayer dielectric 409 is deposited by using thenormal CMOS integrated circuit process, first layer via holes 410 of theintegrated circuit are formed and openings 411 are formed in theinterlayer dielectric 409 at the positions corresponding to the movablemass 405 of the 3-axis acceleration sensor (FIG. 20). Next, the firstlayer via holes 410 and the openings 411 are filled with metal (forexample, tungsten in this case) by using the normal CMOS integratedcircuit process, and the surface thereof is planarized by the CMP. Inthis case, the openings 411 are formed on the patterns of the M1 layerother than the lower electrode 407. Also, in order to prevent theso-called dishing in the CMP, the slit (unremoved pattern of dielectric)is appropriately inserted in the large-area part of the movable mass 405in addition to the fine hole 408 for etching.

Next, through the CMOS integrated circuit process, a second layerinterconnect (M2 layer) 412 of the integrated circuit is formed and themovable mass 405, a movable capacitor plate and a fixed capacitor plateof the 3-axis acceleration sensor are formed from the metal pattern(FIG. 21). The schematic diagram of the pattern of the M2 layer in apart of the 3-axis acceleration sensor is shown in FIG. 26B. As shown inFIG. 26B, movable capacitor plates 412 a are formed on the movable mass405, and fixed capacitor plates 412 b are formed so as to face to themovable capacitor plates 412 a. The fixed capacitor plate 412 b is fixedto the interlayer dielectric 409.

Thereafter, after an interlayer dielectric 413 is deposited by using thenormal CMOS integrated circuit process again, second layer via holes 414of the integrated circuit are formed and openings 415 are formed in theinterlayer dielectric 413 at the positions corresponding to the movablemass 405, the movable capacitor plate 412 a and the fixed capacitorplate 412 b of the 3-axis acceleration sensor (FIG. 22). Next, thesecond layer via holes 414 and the openings 415 are filled with metal(for example, tungsten) by using the normal CMOS integrated circuitprocess, and the surface thereof is planarized by the CMP. In this case,the pattern of the openings 415 is almost the same as that of the M2layer. However, in order to prevent the so-called dishing in the CMP,the slit (unremoved pattern of dielectric) is appropriately inserted inthe large-area part of the movable mass 405.

Next, after a third layer interconnect (M3 layer) 416 of the integratedcircuit is formed by using the normal CMOS integrated circuit processagain, the movable mass 405, the movable capacitor plate 412 a and thefixed capacitor plate 412 b similar to those formed in the M2 layer ofthe 3-axis acceleration sensor are formed from the metal pattern (FIG.23). The patterns of the second layer via holes 414 and the patterns ofthe 3-axis acceleration sensor of the M3 layer are similar to thoseshown in FIG. 26B.

Further, an interlayer dielectric 417 is deposited and the surfacethereof is planarized by the CMP or the like according to need. Then, acavity cover film 419 having a fine hole 418 for forming the cavity atthe position corresponding to the center of the movable mass 405 isformed from a fourth layer interconnect (M4 layer) (FIG. 24). A planview of the cavity cover film 419 of the 3-axis acceleration sensor isshown in FIG. 26C. The fine hole 418 is provided above the center of themovable mass 405, and the movable mass 405 is not present just under thefine hole 418.

Thereafter, the interlayer dielectric around the movable mass 405 isetched and removed through the fine hole 418 to form the cavity 420. Theetching in the depth direction is stopped on the silicon substrate 401.Since the etching proceeds isotropically, the cavity 420 has a roundshape. Finally, the fine hole 418 is filled with a dielectric 421 toseal the cavity 420 (FIG. 25). Since the dielectric 421 thick enough tohave the strength capable of sealing the large cavity 420 is used, thefine hole 418 needs to have a certain size. Also, the relatively thickdielectric 421 for the sealing is formed under the anisotropicdeposition condition.

Next, the operation of the 3-axis acceleration sensor according to thefourth embodiment will be described. As shown in FIG. 26A, in the cavity420, the movable mass 405 is fixed to the interlayer dielectric via theelastic beam 406 formed from the M1 layer. The elastic beam 406 has asquare shape as shown in FIG. 26A, and the elastic beam 406 iselastically deformed and the movable mass 405 is three dimensionallydisplaced in the cavity 420 when a force is applied to the movable mass405. However, the shape shown in FIG. 26A is a mere example and it canbe optimized in various ways, for example, formed into the folded zigzagshape as shown in the second embodiment or the like.

For example, as shown in FIG. 26B, the displacement of the movable mass405 in the cavity 420 in two directions (x and y directions) in the chipsurface is detected as the change in capacitance between the movablecapacitor plate 412 a formed from the M2 layer, the second layer viahole 414 and the M3 layer in a part of the movable mass 405 and thefixed capacitor plate 412 b (formed from the same layer as the movablecapacitor plate 412 a) fixed to the interlayer dielectric and protrudingto the cavity 420. The configuration of the movable capacitor plate 412a and the fixed capacitor plate 412 b and the detection principle arethe same as those of the second embodiment.

The displacement in the direction vertical to the chip surface (zdirection) is detected by detecting the change in capacitance between alower electrode 407 fixed to the interlayer dielectric of the M1 layerjust below a part of the movable mass 405 which is formed from the M2 ormore layers and the movable mass 405.

The fixed capacitor plates 412 b (lower electrode 407) for each of thex, y and z directions and the movable mass 405 are electricallyconnected independently to the signal processing integrated circuit onthe same silicon substrate 401. When the movable mass 405 moves inarbitrary three directions due to the acceleration, the distance betweenthe movable capacitor plate 412 a and the fixed capacitor plate 412 b orbetween the movable mass 405 and the lower electrode 407 is changed andthe interelectrode capacitance is changed. By detecting the change incapacitance in the signal processing integrated circuit (capacitancedetecting circuit), the acceleration is detected.

The elastic beam 406 is designed so that the base part thereof issufficiently thick in the cavity to prevent the elastic deformation evenwhen the acceleration is applied to the mass (fixed part). On the otherhand, the center part of the beam is designed so as to have the smallerwidth in comparison to that of the base part and a sufficient lengthbecause of its folded shape, and the desired elastic deformation occurswhen a predetermined acceleration is applied (elastically deformablepart). Therefore, the mechanical characteristics are determined only bythe planar pattern shape and the thickness of the elastic beam 406 andthe movable mass 405 exposed in the cavity 420, and do not depend on thedimensions and the shape of the cavity 420. Since the dimensionalaccuracy of the elastic beam 406 and the movable mass 405 is determinedby the dimensional accuracy of the patterns of the interconnect layerand the via layer, it is very accurate. Meanwhile, since the dimensionsand the shape of the cavity 420 are determined by the etching of theinterlayer dielectric, the accuracy thereof is not so high. However, itdoes not influence the mechanical characteristics of the 3-axisacceleration sensor according to the fourth embodiment. Also, in thefourth embodiment, since the elastic beam 406 and the movable capacitorplate 412 a are formed in the different interconnect layers, they can beoptimally designed regardless of the restrictions of the planararrangement.

Also, a protrusion is formed in a part of the M2 layer pattern of themovable mass 405, and this protrusion is placed so as to overlap with apart of the patterns of the M1 layer and the M3 layer protruding fromthe interlayer dielectric to the cavity 420 (not shown). By doing so,when the movable mass 405 moves largely up and down, the above-describedprotrusion of the movable mass 405 and the protruding parts of the M1layer and the M3 layer are collided with each other, and the movablerange of the movable mass 405 is limited. Also, since the protrusion andthe protruding parts are deformed when they are collided, the impact atthe collision is reduced. Therefore, the impact resistance and thereliability can be improved in the fourth embodiment.

Since the movable mass is formed from a plurality of interconnect layersin the fourth embodiment, the mass of the movable mass can be increasedand the detection sensitivity of the 3-axis acceleration sensor can beimproved.

Note that the elastic beam 406 can be designed in various ways. In thefourth embodiment, the elastic beam 406 is formed of only the M1 layer.However, it is also possible to form it from all of the M1 layer, thefirst layer via hole 410, the M2 layer, the second layer via hole 414and the M3 layer or the arbitrary combination thereof. For example, theelastic beam and the movable capacitor plate shown in the secondembodiment can be formed by using all of them. Alternatively, threeelastic beams 406 as shown in FIG. 27A can be formed from only theinterconnect layers of the M1 layer, the M2 layer and the M3 layer. Inthis manner, the sensitivity (deformability) to the acceleration (force)in the longitudinal direction (z direction) is increased. In addition,as shown in FIG. 27B, it is also possible to form the elastic beam 406so as to have the folded zigzag shape in the longitudinal direction. Bydoing so, the deformation in the longitudinal direction (z direction) isfurther facilitated. The shape, dimensions and film thickness of themovable mass 405 and the plastic beam 406 are designed from theviewpoint of the desired acceleration range to be detected and theimpact resistance.

Furthermore, it is also possible to further increase the mass of themovable mass by additionally forming films made of other materials asthe movable mass 405. More specifically, the material of the movablemass 405 in the fourth embodiment is not limited to the interconnectmaterial of the integrated circuit, but the other inorganic or organicmaterial is also available. However, it is necessary to use the materialnot removed by the etching of the interlayer dielectric. When an oxidefilm is used as the interlayer dielectric, various metal films such as asilicon-germanium film (SiGe film), a silicon nitride film (SiN film), asilicon oxide film, a single crystal silicon film, an amorphous siliconfilm, a polysilicon film and a polyimide film are also available.Further, a film other than oxide films can be used as the interlayerdielectric as described below.

The manufacturing process of a structure in which a thick film isadditionally formed to the movable mass in the 3-axis accelerationsensor according to the fourth embodiment will be shown in FIG. 28 toFIG. 33.

On the structure formed through the process similar to that shown inFIG. 18 to FIG. 23, a thick resist layer 425 is coated, and openings 426are formed on the movable mass 405 formed from the M3 layer through thenormal exposure and development process (FIG. 28). Next, a nickel (Ni)film 427 is formed in the openings 426 by the electroless plating (FIG.29) (After forming the nickel film, the surface is polished ifnecessary.).

Thereafter, the thick resist layer 425 is removed to expose the nickelfilm 427 to be a thick movable mass structure on the movable mass 405formed from the M3 layer (FIG. 30). Furthermore, a polyimide film 428 iscoated so as to cover the nickel film 427 and the thermal treatment isperformed. Thereafter, a tungsten (W) thin film is formed as a cavitycover film 429 by the sputtering (FIG. 31).

After forming fine holes 430 for etching through the normal exposuremethod in the tungsten thin film (cavity cover film 429), the polyimidefilm 428 around the nickel film 427 is etched and removed through thefine holes 430 (FIG. 32). Then, the interlayer dielectric around themovable structure formed from the underlying interconnect film is etchedand removed to form a cavity 431. Thereafter, the fine holes 430 foretching are filled with a dielectric 432 to seal the cavity 431 (FIG.33).

As described above, since it is possible to form the movable mass 405including the nickel film 427, it is possible to further increase themass of the movable mass 405. Therefore, the detection sensitivity ofthe 3-axis acceleration sensor can be further improved.

Note that, also in the fourth embodiment, the mechanical structure ofthe acceleration sensor can be formed and the cavity can be formed andsealed through the CMOS process. Therefore, the advantages similar tothose of the first embodiment can be realized.

Fifth Embodiment

In this fifth embodiment, an example in which an integral structurecomposed of a plurality of multilayer interconnects is used will bedescribed. In the structure according to the fifth embodiment, a movablepart composed of multilayer interconnects and covered with a dielectricsuch as an oxide film is fixed to an interlayer film surrounding thecavity by an elastic beam similarly having the interconnect structuretherein and covered with a dielectric such as an oxide film in thecavity formed in the interlayer dielectrics. In the embodimentsdescribed above, one movable part is composed of one type of contiguousconductors. Therefore, it has only one electrical function as oneelectrode or interconnect. However, in this fifth embodiment, since itis possible to introduce a plurality of independent interconnects in thestructure, more complicated actuation of the movable part and the signaldetection can be realized.

FIG. 34 to FIG. 39 are schematic diagrams for describing a manufacturingprocess of an angle rate sensor (vibration gyroscope) according to thefifth embodiment.

First, through the normal CMOS integrated circuit process, signalprocessing transistors 502 of the vibration gyroscope and contact holes503 are formed on a silicon substrate 501 (FIG. 34). Next, by using theCMOS integrated circuit process, a first layer interconnect (M1 layer)504 of the integrated circuit is formed, and a sacrificial layer 506 isformed in a region corresponding to the cavity below a movable mass 505of the vibration gyroscope. Next, after depositing an interlayerdielectric 507, first layer via holes 508 of the integrated circuit areformed, and openings 509 are formed in the regions corresponding to thecavity surrounding the movable mass 505 of the vibration gyroscope (FIG.35). Next, by using the normal CMOS integrated circuit process, metal(for example, tungsten in this case) is filled in the first layer viaholes 508 and the openings 509, and the surface thereof is planarized bythe CMP.

Subsequently, by using the normal CMOS integrated circuit process,second layer interconnects (M2 layer) 510 of the integrated circuit areformed, and a sacrificial layer 511 is formed in a region correspondingto the cavity surrounding the movable mass 505 and beams (not shown) ofthe vibration gyroscope. Also, an interconnect 512 is formed in themovable mass 505 and the beams. Subsequently, after depositing aninterlayer dielectric 513, second layer via holes 514 of the integratedcircuit are formed, and openings 515 are formed in the regioncorresponding to the cavity surrounding the movable mass 505 of thevibration gyroscope. Simultaneously, a via hole 516 for connecting theupper and lower interconnects in the movable mass 505 (and in the beamsaccording to need) is formed (FIG. 36).

Next, by using the normal CMOS integrated circuit process, a third layerinterconnect (M3 layer) 517 of the integrated circuit is formed, and asacrificial layer 518 is formed in the region corresponding to thecavity surrounding the movable mass 505 and the beams of the vibrationgyroscope. Simultaneously, an interconnect 519 is formed in the movablemass 505 and the beams. At this time, a part of the interconnect 519 isnot connected to the interconnect 512 and is formed as an independentinterconnect. More specifically, a plurality of independent movableinterconnects are formed in the movable mass 505.

Similarly, after depositing an interlayer dielectric 520, third layervia holes 521 of the integrated circuit are formed, and an opening 522is formed in the region corresponding to the cavity surrounding themovable mass 505 of the vibration gyroscope (FIG. 37). Next, by usingthe normal CMOS integrated circuit process, a fourth layer interconnect(M4 layer) 523 of the integrated circuit is formed, and a sacrificiallayer 524 is formed in the region corresponding to the cavity on themovable mass 505 of the vibration gyroscope. Furthermore, afterdepositing a dielectric, an interlayer dielectric 526 having fine holes525 for forming cavity is formed (FIG. 38).

Thereafter, sacrificial layers 506, 511, 518 and 524 formed from theinterconnect materials are etched and removed through the fine holes 525to form the cavity 527. Finally, the fine holes 525 for etching arefilled with a dielectric 528 to seal the cavity (FIG. 39). Theinterconnects and the sacrificial layers are formed of, for example, analuminum film. However, a tungsten film is also available.

An Al etching solution used for the etching of the sacrificial layershas the high selectivity to the interconnects. Therefore, when etchingthe sacrificial layers, the removal rate of the dielectric (oxide film)on the surfaces of the movable mass 505 and the beams formed in thecavity 527 is extremely low. In this manner, the movable mass 505 inwhich a plurality of independent interconnects are formed can be formed.

Next, the configuration of the angle rate sensor (vibration gyroscope)formed through the above-described manufacturing process will bedescribed with reference to FIG. 40.

A frame structure 531 is formed in the cavity 530. This frame structure531 is fixed to the interlayer dielectric 533 surrounding the cavity 530via beams 532 with rigidity in a detection axis (y) direction extremelyhigher than that in an actuation axis (x) direction. More specifically,the frame structure 531 is easily vibrated in the actuation (x)direction but hardly vibrated in the detection (y) direction. Inside theframe structure 531, the movable mass 534 is fixed to the framestructure 531 via beams 535 with rigidity in an actuation axis (x)direction extremely higher than that in a detection axis (y) direction.

A comb-shaped first actuation electrode 536 fixed to the interlayerdielectric 533 surrounding the cavity 530 is connected to thepredetermined LSI interconnect. A comb-shaped second actuation electrode537 fixed to the frame structure 531 is connected to the predeterminedLSI interconnect outside the cavity 530 via the interconnect in the beam532. The alternating voltage is applied between the first actuationelectrode 536 and the second actuation electrode 537 by an oscillator538.

A comb-shaped first detection electrode 539 fixed to the frame structure531 and a second detection electrode 540 electrically independent fromthe electrode 539 are connected to the predetermined LSI interconnectprovided outside the cavity 530 via the interconnect in the beam 532.

A comb-shaped third detection electrode 541 fixed to the movable mass534 is connected to the predetermined LSI interconnect provided outsidethe cavity 530 via the interconnect in the beam 535, the frame structure531 and the interconnect in the beam 532. An electrostatic capacitancedetecting circuit 542 is connected between the first detection electrode539 and the third detection electrode 541, and an electrostaticcapacitance detecting circuit 543 is connected between the seconddetection electrode 540 and the third detection electrode 541.

All of the electrodes described above are covered with a dielectric.Also, all of the electrode described above are formed from the stackedfilms of the M2 layer and the M3 layer. The interconnect connected tothe second actuation electrode 537 is formed from the M3 layer and theother interconnects connected to the other electrodes are all formedfrom the M2 layer.

Next, the operation of the vibration gyroscope according to the fifthembodiment will be described with reference to FIG. 41. Hereinafter, theactuation axis and the detection axis are considered as the coordinatesystem fixed to the cavity 530. First, by applying the alternatingvoltage between the first actuation electrode 536 and the secondactuation electrode 537, the frame structure 531 is vibrated in theactuation axis direction. At this time, since the beam 535 connectingthe frame structure 531 and the movable mass 534 has the high rigidityin the actuation direction, the movable mass 534 is also vibrated in theactuation axis direction together with the frame structure 531 (FIG.41A).

Next, when the rotation around the axis vertical to the actuation axisand the detection axis (axis vertical to the paper of FIG. 41) occurs,the movable mass 534 starts to vibrate in the detection axis directiondue to the Coriolis force. At this time, since the beam 532 which fixesthe frame structure 531 to the surrounding surface of the cavity 530 hasthe high rigidity in the detection axis direction, the frame structure531 is not vibrated in the detection axis direction. Therefore, thethird detection electrode 541 moves in the detection axis directionrelative to the first detection electrode 539 and the second detectionelectrode 540, and the capacitance between the third detection electrode541 and the first detection electrode 539 or the capacitance between thethird detection electrode 541 and the second detection electrode 540 ischanged. By detecting the change in capacitance, the Coriolis force ismeasured, and the angle rate is detected (FIG. 41B).

In the vibration gyroscope according to the fifth embodiment, since aplurality of independent interconnects can be formed in the structure,it is possible to connect independent circuits to the structure.Therefore, since it is unnecessary to perform the separation of thedetected signals in the vibration direction, the extremely highlyaccurate detection of an angle rate can be realized and the signalprocessing can be greatly simplified. Note that, also in the fifthembodiment, the structure of the vibration gyroscope can be formed andthe cavity can be formed and sealed through the CMOS process. Therefore,the advantages similar to those of the first embodiment can be realized.

Sixth Embodiment

In this sixth embodiment, an example in which a MEMS structure is formedthrough the process other than the interconnect process and a cavity isformed and sealed for the structure through the interconnect processwill be described. As described in the foregoing embodiments, in thecase where an interconnect material, that is, metal is used to formbeams and a movable part, when the MEMS structure is applied and used asa vibration part, the vibration value Q is small due to thecharacteristics of the metal material. In this case, a material capableof obtaining the relatively large vibration value Q such as silicon (Si)or the like is suitable. In the sixth embodiment, an example in whichthe structure of the vibration gyroscope formed through the SOI (SiliconOn Insulator) process is sealed through the interconnect process will bedescribed.

FIG. 42 to FIG. 47 are schematic diagrams for describing themanufacturing process of the vibration gyroscope according to the sixthembodiment, and FIG. 48 is a schematic plan view showing the planarconfiguration of each layer of the structure constituting the vibrationgyroscope. First, in order to form the vibration part on the SOIsubstrate 601, openings 604 extending from the surface of the SOIsubstrate 601 to the embedded dielectric 603 are formed in the SOI layer602 around the patterns to be the vibration parts (mass and beam), andthen, the openings 604 are filled with a CVD oxide film (HLD film) 605(FIG. 42).

Next, through the normal CMOS integrated circuit process, transistors606 for actuation and signal processing of the vibration gyroscope andcontact holes 607 are formed on the SOI substrate 601 (FIG. 43). At thistime, a field oxide film 608 is formed on the SOI layer 602 in thevibration part forming region and its adjacent region.

Subsequently, by using the normal CMOS integrated circuit process, afirst layer interconnect (M1 layer) 609 of the integrated circuit isformed, and a detection electrode 610 is formed on the central part ofthe region for forming the vibration part of the vibration gyroscope(FIG. 44). Thereafter, a second layer interconnect (M2 layer) 611 andsubsequent multilayer interconnects are formed through the normal CMOSintegrated circuit process on the integrated circuit. At this time, onlyan interlayer dielectric is deposited on the vibration part formingregion and its adjacent region. After forming the uppermostinterconnect, an interlayer dielectric 612 is further deposited and itssurface is planarized by the chemical mechanical polishing (CMP)according to need. Then, a cavity cover film 614 having fine holes 613for etching is formed on the interlayer dielectric 612 (FIG. 45).

Thereafter, the interlayer dielectric on the vibration part 615, the CVDoxide film 605 embedded in the openings 604 and the embedded dielectric603 of the SOI substrate 601 below the vibration part (mass and beam)615 are etched and removed through the fine holes 613 to form the cavity616 around the vibration part 615 (FIG. 46). The etching in the depthdirection is stopped on the silicon substrate 601 below the embeddeddielectric 603. Finally, the fine holes 613 for etching are filled witha dielectric 617 to seal the cavity 616 (FIG. 47).

In an application using the vibration characteristics of the mechanicalstructure (vibration part) like in the sixth embodiment, the influenceof the gas resistance around the structure is not negligible. Therefore,the cavity 616 is desirably in a vacuum state. However, since the CVDfilm having the isotropic deposition characteristics is used to fill thefine holes 613, the gas pressure at the time of deposition is left inthe cavity 616, and vacuum sealing is difficult. On the other hand,since the forming pressure of the anisotropic deposition film used tofill the larger hole shown in the third embodiment is close to a vacuum,it is possible to form a near-vacuum state. Therefore, similar to thethird embodiment, at least two sizes of holes, that is, larger holes andfine holes are formed in the cavity cover film 614 also in the sixthembodiment. Then, the planar shape of the cavity 616 is defined throughthe fine holes, and the vacuum sealing of the cavity is performedthrough the larger holes. Note that, in the sixth embodiment, differentfrom the third embodiment, the etching of the dielectric formed on thesurface of the structure and the surface hydrophobic treatment are notalways necessary before the sealing of the larger holes.

Next, the configuration of the angle rate sensor (vibration gyroscope)formed through the process described above will be described withreference to FIG. 48. FIG. 48A is a plan view showing the SOI layer, inwhich the vibration gyroscope includes the vibration part 615 having aframe structure 620 and a mass 621, first actuation electrodes 622 fixedto the surface of the cavity 616 and second actuation electrodes 623fixed to the frame structure 620. In the cavity 616, the frame structure620 formed from the SOI layer is fixed to the interlayer dielectric 625surrounding the cavity 616 via beams 624 with rigidity in an actuationaxis (x) direction lower than that in other directions. Morespecifically, the frame structure 620 is easily vibrated in theactuation axis (x) direction but hardly vibrated in the detection axis(direction vertical to the paper of FIG. 48) direction and in therotation axis (y) direction.

Inside the frame structure 620, the mass 621 formed from the SOI layeris fixed to the frame structure 620 via beams 626 with rigidity in theactuation axis direction and rotation axis direction sufficiently higherthan that in other directions. More specifically, the mass 621 is easilyvibrated in the detection axis (z) direction but hardly vibrated in theother detections.

Two types of electrodes such as the first actuation electrodes 622 andthe second actuation electrodes 623 are formed from a diffusion layerformed by the ion implantation and are connected to the integratedcircuits for actuation and signal processing via the contact holes andthe multilayer interconnects. The shape of these electrodes is definedby the etching when forming the openings 604. By applying alternatingvoltage between the first actuation electrode 622 and the secondactuation electrode 623, the vibration part 615 is vibrated in theactuation axis direction of FIG. 48.

FIG. 48B is a plan view showing the detection electrode 610 formed fromthe M1 layer. By detecting electrostatic capacitance between thedetection electrode 610 and the mass 621, the displacement of thevibration part in the detection axis direction (direction vertical tothe paper of FIG. 48 or the substrate surface of the chip) is detected.The opposing area between the mass 621 and the detection electrode 610is not changed even when the mass 622 is vibrated (moved) in theactuation axis direction. Therefore, the electrostatic capacitancebetween the mass 621 and the detection electrode 610 almost depends ononly the space (distance) therebetween.

The shape of the beam 626 is designed so that a base part thereof issufficiently thick and it is not displaced by the designed range ofvibration. Therefore, since the mechanical characteristics aredetermined only by the planar shape and the thickness of the mass 621exposed in the cavity 616 and do not depend on the dimensions and theshape of the cavity 616, it is very accurate.

Next, the operation of the angle rate sensor according to the sixthembodiment will be described with reference to FIG. 49. By applyingalternating voltage between the first actuation electrode and the secondactuation electrode, the frame structure 620 is vibrated in theactuation axis direction. At this time, since the beam 626 connectingthe frame structure 620 and the mass 621 has high rigidity in theactuation axis direction, the mass 621 is vibrated in the actuation axisdirection together with the frame structure 620 (FIG. 49A). Next, whenthe rotation occurs around the rotation axis, the mass 621 starts tovibrate in the detection axis direction due to the Coriolis force. As aresult, the electrostatic capacitance between the mass 621 and thedetection electrode 610 is changed. By detecting the change incapacitance, the angle rate is monitored (FIG. 49B).

As described above, the mass 621 is formed from only the SOI layer inthe sixth embodiment. However, it is also possible to further stack acontact layer and multilayer interconnects on the SOI layer as the mass621 in order to increase the mass of the mass 621. The process will bedescribed below in brief.

First, in order to form the vibration part on the SOI substrate 601,openings 604 extending from the surface of the SOI substrate 601 to theembedded dielectric 603 are formed in the SOI layer 602 around thepatterns to be the vibration parts (mass and beam), and then, theopenings 604 are filled with a CVD oxide film (HLD film) 605 (FIG. 50).

Next, through the normal CMOS integrated circuit process, transistors606 for actuation and signal processing of the vibration gyroscope andcontact holes 607 are formed on the SOI substrate 601 (FIG. 51). At thistime, openings 630 are also formed on the SOI layer 602 in the vibrationpart forming region and its adjacent region.

Subsequently, through the normal CMOS integrated circuit process, afirst layer interconnect (M1 layer) 631 and subsequent multilayerinterconnects are formed on the integrated circuit. At this time, themultilayer interconnects 632 constituting the vibration part are formedalso on the openings 630. Then, after forming the interlayer dielectric633, a third layer interconnect (M3 layer) 634 is formed on theintegrated circuit, and detection electrodes 635 are formed on theregion for forming the vibration part. In this embodiment, the detectionelectrode 635 is formed from the same layer as the M3 layer. However, itis also possible to form the detection electrode 635 from an appropriatelayer in the multilayer interconnects. Next, after forming an interlayerdielectric 636 on the M3 layer and the detection electrodes 635, acavity cover film 638 having fine holes 637 for etching is formed on theinterlayer dielectric 636 (FIG. 52).

Thereafter, the interlayer dielectric on the vibration part 615, the CVDoxide film 605 embedded in the openings 604 and the embedded dielectric603 of the SOI substrate 601 below the vibration part (mass and beam)615 are etched and removed through the fine holes 637 to form the cavity639 around the vibration part 615 (FIG. 53). The etching in the depthdirection is stopped on the silicon substrate 601 below the embeddeddielectric 603. Finally, the fine holes 637 for etching are filled witha dielectric 640 to seal the cavity 639 (FIG. 54).

As described above, since the multilayer interconnects are used to formthe vibration part 615 in addition to the SOI layer, it is possible toincrease the mass of the vibration part 615, and the detectionsensitivity of the vibration gyroscope can be improved.

It is also possible to use a thick polysilicon film to form thevibration part instead of the SOI layer. In this case, by using thesubstrate formed by sequentially stacking an oxide film and apolysilicon film with a predetermined thickness on a silicon substrateinstead of the SOI substrate, the sixth embodiment can be appliedwithout modification.

The patterning of the vibration part composed of an SOI layer or a thickpolysilicon film, that is, the definition of the planar shape of thevibration part and its peripheral part by the etching and the embeddingof the oxide film (sacrificial film) to the etched part can be performedeither before or after forming the transistors of the integratedcircuit.

The first point of the sixth embodiment is that the vibration partformed from a SOI layer or formed by stacking a SOI layer and multilayerinterconnects and the detection electrodes formed from the multilayerinterconnects are combined to constitute the angle rate sensor. Also,the second point thereof is that the vibration part of the angle ratesensor is placed in the cavity formed and sealed in the interlayerdielectric, which does not define the design characteristics of theangle rate sensor. Therefore, the planar shape and the arrangementdescribed above are mere schematic examples, and the modification andthe design optimization can be made appropriately.

Note that, also in the sixth embodiment, the formation of the mechanicalstructure of the vibration gyroscope and the formation and sealing ofthe cavity can be performed through the normal CMOS process. Therefore,the advantages similar to those of the first embodiment can be realized.

Next, the application examples of the MEMS described in theabove-described embodiments will be described in the following seventhto ninth embodiments.

Seventh Embodiment

The entire configuration of a gas pressure monitoring system for tireusing the MEMS will be described with reference to FIG. 55 to FIG. 57.FIG. 55 is a diagram showing the configuration of the gas pressuremonitoring system for tire seen from the bottom surface of anautomobile, and it is comprised of a vehicle 701, tires 702 a to 702 dprovided on left front, right front, left rear and right rear of thevehicle, tire pressure measurement modules 703 a to 703 d provided toeach of the tires 702 a to 702 d, and an in-vehicle unit 704. Also, FIG.56 and FIG. 57 are block diagrams of the tire pressure measurementmodule 703 (703 a to 703 d) and the in-vehicle unit 704, respectively.

FIG. 56 is a block diagram of the tire pressure measurement module 703,and is comprised of one IC chip 705 and a battery 706 with the voltageof VBAT for supplying the power to the IC chip 705. The IC chip 705includes a pressure sensor circuit 707, a temperature sensor circuit708, an acceleration sensor circuit 709, analog-digital (A/D) conversioncircuits 710, 711 and 712, a data processing control unit 713, a memorycircuit 714, a data transmission circuit 715 and a data receiver circuit716. In this case, the pressure sensor circuit 707 and the temperaturesensor circuit 708 are the circuits for measuring the gas pressure andthe temperature of the tires, respectively. Also, the accelerationsensor circuit 709 is the circuit for determining whether the tires arerotated. In the pressure sensor circuit 707 and the acceleration sensorcircuit 709, the MEMS (micro machine) constituting the pressure sensorand the acceleration sensor are formed. More specifically, in the ICchip 705, in addition to the integrated circuit, the MEMS to be thepressure sensor and the acceleration sensor are formed. As the pressuresensor formed in the pressure sensor circuit 707 and the accelerationsensor formed in the acceleration sensor circuit 709 according to theseventh embodiment, for example, the pressure sensor and theacceleration sensor described in the first, second and fourthembodiments are used.

In the MEMS formed in the IC chip 705, as described in the foregoingembodiments, the cavity can be formed and sealed through the normal CMOSprocess. Therefore, the special process for forming and sealing thecavity (packaging process particular to MEMS) which is the major causeof the yield decrease and the manufacturing cost increase in theconventional MEMS manufacturing process becomes unnecessary. As aresult, in the seventh embodiment, it is possible to improve the yield,reduce the manufacturing (packaging) cost and improve the reliability ofthe IC chip 705. In addition, since the structure of the MEMS can beformed simultaneously with the formation of the interconnect of the LSI,the integration with the LSI can be facilitated.

The analog-digital conversion circuits 710, 711 and 712 are the circuitsfor converting the analog voltage value outputted from the pressuresensor circuit 707, the temperature sensor circuit 708 and theacceleration sensor circuit 709 into the digital voltage value.

The data processing control unit 713 (1) inputs the digital voltagevalue converted in the analog-digital conversion circuits 710, 711 and712, (2) performs the correction computing to correct the pressuremeasurement value measured in the pressure sensor circuit 707, (3)changes the control state in accordance with the output from theacceleration sensor circuit 709, (4) outputs the data to the datatransmission circuit 715, (5) receives the data from the data receivercircuit 716, and (6) controls the ON/OFF of the individual powersupplies of the pressure sensor circuit 707, the temperature sensorcircuit 708, the acceleration sensor circuit 709, the data transmissioncircuit 715 and the data receiver circuit 716 in response to the ENsignals.

The memory circuit 714 is the circuit for registering the correctionvalue for correcting the pressure measurement value measured in thepressure sensor circuit 707 and the ID of the tire pressure measurementmodule 703. Note that the ID number (for example, 32 bits) is used toconfirm the tires of one's own car from those of others and thepositions of the tires.

The data transmission circuit 715 is the circuit for performing the RFtransmission of data such as the measurement value corrected by thecomputing in the data processing control unit 713 to the in-vehicle unit704 shown in FIG. 55. The frequency of the carrier wave used in this RFtransmission is UHF band, for example, 315 MHz. In this datatransmission, the carrier wave which is ASK modulated or FSK modulatedby the transmitted data is transmitted.

On the other hand, the data receiver circuit 716 is the circuit forperforming the RF reception of data such as the control signal from thein-vehicle unit 704 and it transmits the data to the data processingcontrol unit 713. The frequency of the carrier wave received in the datareceiver circuit 716 is LF band, for example, 125 kHz, and the carrierwave which is ASK modulated by the transmitted data is transmitted.

Antennas 717 and 718 are connected to the data transmission circuit 715and the data receiver circuit 716, respectively. Also, as the battery706 for supplying power to the IC chip 705, a coin type lithium battery(voltage 3 V) is used.

Next, FIG. 57 is a block diagram of the in-vehicle unit 704. As shown inFIG. 57, the in-vehicle 704 is provided with a data processing controlunit 719 for performing the data input/output and calculation of thedata, a data receiver circuit 720, a data transmission circuit 721, anantenna 722 connected to the data receiver circuit 720, an antenna 723connected to the data transmission circuit 721 and a display unit 724for displaying the measurement values and cautions.

The data processing control unit 719 receives the data which is RFtransmitted from the tire pressure measurement module 703 (703 a to 703d) shown in FIG. 55 via the data receiver circuit 720, and it displaysthe pressure measurement values and the caution and the warning of thepressure decrease on the display unit 724. Further, the data processingcontrol unit 719 transmits the control data to the tire pressuremeasurement module 703 (703 a to 703 d) via the data transmissioncircuit 721. Note that the power required in the in-vehicle unit 704 issupplied from the battery (not shown) mounted in the vehicle.

According to the seventh embodiment, since the MEMS formed by using thestandard CMOS process is used to constitute the tire pressuremeasurement module 703 (703 a to 703 d), it is possible to improve theyield and the reliability of the tire pressure measurement module 703(703 a to 703 d). Therefore, it is possible to improve the reliabilityof the gas pressure monitoring system for tire.

Eighth Embodiment

The entire configuration of an anti-skid device for a vehicle using theMEMS will be described with reference to FIG. 58 and FIG. 59. In thiscase, FIG. 58 is a diagram showing the anti-skid device for a vehicleseen from the bottom surface of an automobile, and it is comprised of avehicle 801, tires 802 a to 802 d provided on left front, right front,left rear and right rear of the vehicle, braking force control actuators803 a to 803 d which control the brake provided to each of the tires 802a to 802 d, and an anti-skid control circuit 804 for controlling thebraking force control actuators 803 a to 803 d. Also, FIG. 59 is a blockdiagram of the anti-skid control circuit 804, and the anti-skid controlcircuit 804 has one IC chip 805 and a braking force calculation circuit806.

The IC chip 805 has acceleration sensor circuits 807 and 808 fordetecting the acceleration in the x and y directions of the coordinateaxis shown in FIG. 58 and an angle rate sensor circuit 809 for detectingthe rotation angle rate around the coordinate axis z. The MEMS forconstituting the angle rate sensor and the acceleration sensor areformed in these angle rate sensor circuit 809 and the accelerationsensor circuits 807 and 808. More specifically, in the IC chip 805, theMEMS to be the angle rate sensor and the acceleration sensor are formedin addition to the integrated circuit. As the angle rate sensor formedin the angle rate sensor circuit 809 and the acceleration sensor formedin the acceleration sensor circuits 807 and 808 according to the eighthembodiment, for example, the acceleration sensor described in the firstand second embodiments and the angle rate sensor described in the fifthand sixth embodiments are used.

In the MEMS formed in the IC chip 805, as described in the foregoingembodiments, the cavity can be formed and sealed through the normal CMOSprocess. Therefore, the special process for forming and sealing thecavity (packaging process particular to MEMS) which is the major causeof the yield decrease and the manufacturing cost increase in theconventional MEMS manufacturing process becomes unnecessary. As aresult, in the eighth embodiment, it is possible to improve the yield,reduce the manufacturing (packaging) cost and improve the reliability ofthe IC chip 805. In addition, since the structure of the MEMS can beformed simultaneously with the formation of the interconnect of the LSI,the integration with the LSI can be facilitated.

Furthermore, the IC chip 805 has analog-digital (A/D) conversioncircuits 810, 811 and 812, a data correction circuit 813 and a memorycircuit 814. The analog-digital (A/D) conversion circuits 810, 811 and812 are the circuits for converting the analog voltage value outputtedfrom the angle rate sensor circuit 809 and the acceleration sensorcircuits 807 and 808 into the digital voltage value. The data correctioncircuit 813 is the circuit for correcting the difference from the idealoutput characteristics of the angle rate sensor circuit 809 and theacceleration sensor circuits 807 and 808, and the coefficient of thecorrection value is registered in the memory circuit 814 in advance.

The configuration of the anti-skid device according to the eighthembodiment has been described above. Next, the operation thereof will bedescribed below in brief. First, the angle rate sensor circuit 809 andthe acceleration sensor circuits 807 and 808 formed on the IC chip 805detect the angle rate and the acceleration applied to the vehicle. Inaddition, a handling angle (steering angle) is also detected.Furthermore, the vehicle speed and the brake operation amount are alsodetected from outside. Then, when information such as the angle rate,the acceleration, the handling angle, the vehicle speed and the brakeoperation amount is inputted to the anti-skid control circuit 804, thecontrol signals are outputted from the anti-skid control circuit 804 tothe braking force control actuator 803 (803 a to 803 d) so as to preventthe skid of the vehicle. Then, the braking force of the tires 802 a to802 d is controlled by the braking force control actuator 803 (803 a to803 d). In this manner, it is possible to prevent the skid of thevehicle.

According to the eighth embodiment, since the MEMS formed by using thestandard CMOS process is used to form the IC chip 805, it is possible toimprove the yield and the reliability of the IC chip 805. Therefore, itis possible to improve the reliability of the anti-skid device forvehicle.

Ninth Embodiment

The entire configuration of an air suspension control unit for vehiclewill be described with reference to FIGS. 60 and 61. In this case, FIG.60 is a block diagram showing the air suspension control unit 901, andit is comprised of one IC chip 902, a spring constant/damping constantcalculation circuit 903 and an actuator for controlling the innerpressure of the air suspension. The IC chip 902 has a pressure sensorcircuit 905, a temperature sensor circuit 906, an acceleration sensorcircuit 907, analog-digital (A/D) conversion circuits 908, 909 and 910,a data correction circuit 911 and a memory circuit 912. In this case,the pressure sensor circuit 905 and the temperature sensor circuit 906are the circuit for measuring the gas pressure and the temperature inthe air suspension, respectively. Also, the acceleration sensor circuit907 is the circuit for detecting the acceleration in the verticaldirection from the vehicle so as to detect the movement in the verticaldirection of the vehicle mainly due to the bumps on the road. In thepressure sensor circuit 905 and the acceleration sensor circuit 907, theMEMS constituting the pressure sensor and the acceleration sensor areformed. More specifically, in the IC chip 902, in addition to theintegrated circuit, the MEMS to be the pressure sensor and theacceleration sensor are formed. As the pressure sensor formed in thepressure sensor circuit 905 and the acceleration sensor formed in theacceleration sensor circuit 907 according to the ninth embodiment, forexample, the pressure sensor and the acceleration sensor described inthe first, second and fourth embodiments are used.

In the MEMS formed in the IC chip 902, as described in the foregoingembodiments, the cavity can be formed and sealed through the normal CMOSprocess. Therefore, the special process for forming and sealing thecavity (packaging process particular to MEMS) which is the major causeof the yield decrease and the manufacturing cost increase in theconventional MEMS manufacturing process becomes unnecessary. As aresult, in the ninth embodiment, it is possible to improve the yield,reduce the manufacturing (packaging) cost and improve the reliability ofthe IC chip 902. In addition, since the structure of the MEMS can beformed simultaneously with the formation of the interconnect of the LSI,the integration with the LSI can be facilitated.

The analog-digital conversion circuits 908, 909 and 910 are the circuitsfor converting the analog voltage value outputted from the pressuresensor circuit 905, the temperature sensor circuit 906 and theacceleration sensor circuit 907 into the digital voltage value. The datacorrection circuit 911 is the circuit for correcting the difference fromthe ideal output characteristics of the pressure sensor circuit 905 andthe acceleration sensor circuit 907, and the coefficient of thecorrection value is registered in the memory circuit 912 in advance.

FIG. 61 is a side view of the vehicle, which shows the configuration ofan automobile in which the air suspension is mounted. In FIG. 61, theautomobile is provided with a vehicle body 913, tires 914 a and 914 bprovided on right front and right rear of the vehicle (only one side isshown here) and air suspensions 915 a and 915 b in which the airsuspension control unit 901 (901 a and 901 b) is mounted and air springsfor suspending the vehicle body 913 on the tires 914 a and 914 b areused.

The air suspension control unit 901 has the configuration as describedabove, and the operation thereof will be described below in brief.

First, the pressure and the acceleration applied to the vehicle aredetected by the pressure sensor circuit 905 and the acceleration sensorcircuit 907 formed on the IC chip 902. Then, the vehicle speed and thelike are detected from outside. Thereafter, when the air suspensioncontrol unit 901 receives information such as the pressure, theacceleration and the vehicle speed, the control signal is outputted tothe actuator 904 so as to prevent the vibration of the vehicle in thevertical direction. As a result, the spring constant and the dampingconstant of the respective air suspensions 915 a and 915 b arecontrolled to reduce the vibration of the vehicle in the verticaldirection.

According to the ninth embodiment, since the MEMS formed by using thestandard CMOS process is used to form the IC chip 902, it is possible toimprove the yield and the reliability of the IC chip 902. Therefore, itis possible to improve the reliability of the anti-skid device forvehicle.

In the foregoing, the invention made by the inventors of the presentinvention has been concretely described based on the embodiments.However, it is needless to say that the present invention is not limitedto the foregoing embodiments and various modifications and alterationscan be made within the scope of the present invention.

It is also possible to form the structure of MEMS described in theforegoing embodiments so as to contain any one of a metal film, asilicon-germanium film, a silicon nitride film, a silicon oxide film, asingle crystal silicon film, a polysilicon film, an amorphous siliconfilm and a polyimide film.

The integrated MEMS according to the present invention can be utilizedin, for example, an automobile, a mobile device, an amusement machine, awireless device, an information appliance, a computer and the like.

1. An integrated micro electromechanical system, comprising: asemiconductor substrate; a plurality of transistors formed on saidsemiconductor substrate; an interlayer dielectric formed over saidplurality of transistors; a cavity formed in said interlayer dielectric;an acceleration sensor formed in said cavity, and having a movable mass,a movable capacitor plate fixed to said movable mass, and a fixedcapacitor plate fixed to said interlayer dielectric and opposed to saidmovable capacitor plate; and an etching stopper film to which a part ofan upper surface has been exposed in bottom of said cavity, wherein saidmovable mass, said movable capacitor plate and said fixed capacitorplate are composed of a first interconnect layer, wherein said etchingstopper form is composed of a second interconnect layer between saidplurality of transistors and said first interconnect layer, and whereinsaid etching stopper film functions as an electric shield between saidacceleration sensor and an integrated circuit including said pluralityof transistors.
 2. An integrated micro electro-mechanical systemaccording to claim 1, further comprising: a pad electrically connectedto said transistor, composed of said first interconnect layer.
 3. Anintegrated micro electromechanical system according to claim 1, whereinsaid first interconnect layer is thicker than said second interconnectlayer.
 4. An integrated micro electro-mechanical system according toclaim 2, wherein said first interconnect layer is thicker than saidsecond interconnect layer.